Earth-boring tools for forming wellbores in subterranean earth formations may include cutting elements secured to a body. For example, fixed-cutter, earth-boring rotary drill bits (also referred to as “drag bits”) include cutting elements that are fixedly attached to a body of the drill bit. Similarly, roller cone earth-boring rotary drill bits include cones that are mounted on bearing pins extending from legs of a body such that each cone is capable of rotating about the bearing pin on which it is mounted. Cutting elements may be mounted to each cone of the drill bit.
The cutting elements used in such earth-boring tools are often polycrystalline diamond compact (often referred to as “PDC”) cutting elements, also termed “cutters.” PDC cutting elements include a polycrystalline diamond (PCD) material, which may be characterized as a superabrasive or superhard material. Such polycrystalline diamond materials are formed by sintering and bonding together small diamond grains (e.g., diamond crystals), termed “grit,” under conditions of high temperature and high pressure in the presence of a catalyst material to form a polycrystalline diamond material. The polycrystalline diamond material is frequently in the shape of a disc, also called a “diamond table.” The processes used to form polycrystalline diamond material are often referred to as high temperature/high pressure (“HTHP”) processes.
PDC cutting elements also frequently feature a substrate to which the polycrystalline diamond compact is secured. The cutting element substrate may be formed of a ceramic-metallic composite material (i.e., a cermet), such as, for example, cobalt-cemented tungsten carbide. In some instances, the polycrystalline diamond table may be formed on the substrate, for example, during the HTHP sintering process. In such instances, cobalt or other metal solvent catalyst material in the cutting element substrate (e.g., a metal matrix of the ceramic-metallic composite material) may be swept among the diamond grains during sintering and serve as a catalyst material for forming a diamond table from the diamond grains. Powdered catalyst material may also be mixed with the diamond grains prior to sintering the grains together in an HTHP process. In other methods, however, the diamond table may be formed separately from the cutting element substrate and subsequently attached thereto.
To reduce problems associated with differences in thermal expansion and chemical breakdown of the diamond crystals in PDC cutting elements, “thermally stable” polycrystalline diamond compacts (which are also known as thermally stable products or “TSPs”) have been developed. Such a thermally stable polycrystalline diamond compact may be formed by removing catalyst material out from interstitial spaces among the interbonded grains in the diamond table (e.g., by leaching the catalyst material from the diamond table using a corrosive material, such as an acid). Diamond tables that have been at least substantially fully leached are relatively more brittle and vulnerable to shear, compressive, and tensile stresses than are unleached diamond tables. In addition, it may be difficult to secure a completely leached diamond table to a supporting substrate. To provide cutting elements having diamond tables that are more thermally stable relative to unleached diamond tables, but that are also relatively less brittle and vulnerable to shear, compressive, and tensile stresses than fully leached diamond tables, cutting elements have been provided that include a diamond table in which the catalyst material has been leached from only a portion or portions of the diamond table. For example, it is known to leach catalyst material from the cutting face, from the side of the diamond table, or both, to a desired depth within the diamond table, but without leaching all of the catalyst material out from the diamond table.